The present invention relates to highway guardrail systems having a guardrail mounted on posts, and more particularly, to guardrail end treatments designed to meet applicable federal and state safety standards including but not limited to crash worthiness requirements.
Along most highways there are hazards which present substantial danger to drivers and passengers of vehicles if the vehicles leave the highway. To prevent accidents from a vehicle leaving a highway, guardrail systems are often provided along the side of the highway. Experience has shown that guardrails should be installed such that the end of a guardrail facing oncoming traffic does not present another hazard more dangerous than the original hazard requiring installation of the associated guardrail systems. Early guardrail systems often had no protection at the end facing oncoming traffic. Sometimes impacting vehicles became impaled on the end of the guardrail causing extensive damage to the vehicle and severe injury to the driver and/or passengers. In some reported cases, the guardrail penetrated directly into the passenger""s compartment of the vehicle fatally injuring the driver and passengers.
Various highway guardrail systems and guardrail end treatments have been developed to minimize the consequences resulting from a head-on impact between a vehicle and the extreme end of the associated guardrail. One example of such end treatments includes tapering the ends of the associated guardrail into the ground to eliminate potential impact with the extreme end of the guardrail. Other types of end treatments include breakaway cable terminals (BCT), vehicle attenuating terminals (VAT), the SENTRE end treatment, and breakaway end terminals (BET).
It is desirable for an end terminal assembly installed at one end of a guardrail facing oncoming traffic to attenuate any head-on impact with the end of the guardrail and to provide an effective anchor to redirect a vehicle back onto the associated roadway after a rail face impact with the guardrail downstream from the end terminal assembly. Examples of such end treatments are shown in U.S. Pat. No. 4,928,928 entitled Guardrail Extruder Terminal, and U.S. Pat. No. 5,078,366 entitled Guardrail Extruder Terminal.
A SENTRE end treatment often includes a series of breakaway steel guardrail support posts and frangible plastic containers filled with sandbags. An impacting vehicle is decelerated as the guardrail support posts release or shear and the plastic containers and sandbags are compacted. A cable is often included to guide an impacting vehicle away from the associated guardrail.
A head-on collision with a guardrail support post located at the end of a guardrail system may result in vaulting the impacting vehicle. Therefore, guardrail end treatments often include one or more breakaway support posts which will yield or shear upon impact by a vehicle. Examples of previously available breakaway posts are shown in U.S. Pat. No. 4,784,515 entitled Collapsible Highway Barrier, and U.S. Pat. No. 4,607,824 entitled Guardrail End Terminal. Posts such as shown in the ""515 and the ""824 Patents include a slip base with a top plate and a bottom plate which are designed to not yield upon lateral impact. When sufficient axial impact force is applied to the upper portion of the associated post, the top plate and the bottom plate will slide relative to each other. If a vehicle contacts the upper part of the post, the associated impact forces tend to produce a bending moment which may reduce or eliminate any slipping of the top plate relative to the bottom plate. Also, improper installation of the top plate relative to the bottom plate, such as over tightening of the associated mechanical fasteners, may prevent proper functioning of the slip base. A breakaway support post is also shown in U.S. Pat. No. 5,503,495 entitled Thrie-Beam Terminal with Breakaway Post Cable Release.
Wooden breakaway support posts are frequently used to releasably anchor guardrail end treatments and portions of the associated guardrail. Such wooden breakaway support posts, when properly installed, generally perform satisfactorily to minimize damage to an impacting vehicle during either a rail face impact or a head-on impact. However, impact of a vehicle with a wooden breakaway support post may often result in substantial damage to the adjacent soil. Removing portions of a broken wooden post from the soil is often both time consuming and further damages the soil. Therefore, wooden breakaway support posts are often installed in hollow metal tubes, sometimes referred to as foundation sleeves, and/or concrete foundations. For some applications, one or more soil plates may be attached to each metal sleeve to further improve the breakaway characteristics of the associated wooden post. Such metal sleeves and/or concrete foundations are relatively expensive and time consuming to install.
Light poles, sign posts or similar items are often installed next to a roadway with a breakable or releasable connection. For some applications, a cement foundation may be provided adjacent to the roadway with three or more bolts projecting from the foundation around the circumference of the pole. Various types of frangible or breakable connections may be formed between the bolts and portions of the light pole or sign post.
Other possible solutions to the problems discussed are found in U.S. patent application Ser. No. 09/074,496, filed May 7, 1998, entitled Breakaway Metal Post for Highway Guardrail End Treatments, and U.S. Provisional Application No. 60/046,015 filed May 9, 1997, entitled A Breakaway Metal Post for Highway Guardrail End Treatments. These solutions have been adequate for their intended purposes, but are not satisfactory in all respects. For example, previous breakaway support post designs have not included reusable parts. For another example, previous breakaway support post designs have included parts which require extensive machining.
From the foregoing, it may be appreciated that a need has arisen for an apparatus for a breakaway support post for mounting a guardrail thereon as part of a highway guardrail system which is cheaper and more reusable than previous designs. According to one form of the present invention, this need is met by such a breakaway support post which includes an elongated body having an upper portion including a first upper end and a first lower end, and a lower portion including a second upper end and a second lower end. The second lower end is insertable into the soil adjacent to a roadway. The first lower end has a first substantially vertical surface thereon and the second upper end has a second substantially vertical surface thereon. A first arrangement attaches the guardrail to the elongated body adjacent to the first upper end. A second arrangement rotatably couples the upper and lower potions, and releasably secures the upper portion of the elongated body generally aligned with the lower portion of the elongated body, wherein the breakaway support post will resist a rail face impact with the guardrail and wherein an impact with one end of the attached guardrail will tend to rotate the upper portion of the elongated body relative to the lower portion of the elongated body. The second arrangement includes a first plate having a first opening and a second opening therethrough, and having a third substantially vertical surface thereon. A portion of the third substantially vertical surface is disposed against a portion of the first substantially vertical surface. The first plate is secured to the first lower end by a weld. The second arrangement further includes a second plate having a third opening and a fourth opening therethrough, and having a fourth substantially vertical surface thereon. A portion of the fourth substantially vertical surface is disposed against a portion of the second substantially vertical surface. The second plate is secured to the second upper end by a weld. The second plate is disposed adjacent to the first plate so that the first opening is aligned with the third opening, and the second opening is aligned with the fourth opening. A pivot pin portion extends through the first and third openings. The upper portion of the elongated body is rotatable about the pivot pin portion relative to the lower portion of the elongated body. A shear pin portion extends through the second and fourth openings. The shear pin portion is adapted to shear in response to a force to allow pivotal movement of the upper portion relative to the lower portion around the pivot pin portion. The pivot pin portion and the shear pin portion extend in a strong direction approximately perpendicular to the plates. The support post exhibits a high mechanical strength in the strong direction, there also being a weak direction that is generally perpendicular to the strong direction, wherein the support post exhibits a low mechanical strength in the weak direction.
According to a different form of the present invention, a highway guardrail system includes an elongated guardrail. The highway guardrail system further includes a support post having a strong direction generally perpendicular to the guardrail, and a weak direction generally parallel to the guardrail, wherein the support post exhibits a high mechanical strength in the strong direction, and the support post exhibits a lower mechanical strength in the weak direction than in the strong direction, and the support post includes an elongated body having an upper portion and a lower portion, the lower portion being insertable into the soil adjacent to a roadway. The highway guardrail system further includes an attaching arrangement for attaching the guardrail to the support post adjacent to an upper end of the upper portion of the support post and a coupling arrangement for yieldly retaining the upper portion in an upright position relative to the lower portion, the coupling arrangement having a greater resistance to forces exerted on the upper portion in the strong direction than to forces exerted on the upper portion in the weak direction, and wherein in response to a force exerted in the weak direction which is greater than a predetermined amount of force, the coupling arrangement will permit the upper portion to move away from the upright position relative to the lower portion. The highway guardrail system further includes a cable having a first end and a second end, and a releasable arrangement for releasably maintaining the first end of the cable in an initial position relative to the post when the upper portion is in the upright position relative to the lower portion and for permitting the first end of the cable to move away from the initial position when the upper portion moves away from the upright position.